The coating compositions of this invention are dry, free flowing powders that may be used in fusion coating processes. "Fusion coating processes" are herein defined as those coating processes in which a coating powder is distributed over a substrate and heat, supplied from the substrate or an external source, fuses the powder into a continuous film. Examples of fusion coating processes include fluidized bed, electrostatic spraying, hot flocking, and cloud chambers. When the coating powder is based upon heat curing resins, as is the case of the hydroxy-functional resins of this invention, sufficient heat in excess of that required to fuse the powder must be available to cure the coating and fully develop its physical and chemical properties.
Wrinkle finishes are desired in many applications and are commonly applied to office equipment such as typewriters, staplers, dictating equipment, file cabinets, tool boxes, and the like. In addition to being aesthetically pleasing, these finishes have certain utilitarian functions: they hide surface defects of a substrate even when applied in thin films and, having a low gloss, they do not show scratches. Wrinkle finishes, as contemplated for the purposes of this invention, are reticulated, i.e., made up of a pattern of raised veins across the surface and are exemplified by interconnected star-burst patterns, mosaics, and by patterns similar to that of an alligator hide.
Wrinkle finish coatings conventionally are applied from solvent-based paints, usually using two coats, to establish a compound system in which the surface sets up first. When the rest of the coating cures, the resulting shrinkages deform the previously set surface and cause a fine wrinkle pattern to develop on the surface of the coating.
Epoxy resin-based powder coatings having wrinkle finishes are taught in U. S. Pat. No. 4,341,819. The wrinkle pattern is achieved by means of a special curing agent, methylene disalicylic acid, acting upon the epoxy groups of the resin. Because of the rather poor weatherability of epoxy resin coatings, these wrinkle-finish coatings are used almost exclusively on surfaces protected from the weather and are very popular for interior uses. Golownia teaches in U.S. Pat. No. 4,271,277 that catalysis of the curing of a hydroxyl polyester-based powder coating by an amine salt of p-toluene sulfonic acid causes a severe wrinkle in the surface of the cured coat whereas the wrinkle is avoided by the use of an amine salt of cyclohexyl sulfamic acid when the same curing agent, tetra (methoxymethyl) glycoluril, is used. What is needed is a predictable method for forming weatherable wrinkle finish coatings of all colors.